As Coleman said, no, for adding fields, but we removed certain fields for our setup with jQuery so our users wouldn't mis-click.
EDIT: I went back to look at the code, and I remembered that we tried removing the fields with simple jQuery .hide() or .remove(), but realized that the standard classes we were trying to use were used elsewhere so it did more damage than good. In trying to use something like a nth-child selector on the li, we ran into trouble as well, though I can't remember what exactly.
We ended up going the custom tpl route by creating a copy of templates/CRM/common/navigation.js.tpl and placing it in our custom templates directory and commenting out of the "li"'s that we didn't want. Beginning around line 40:
<!-- <li><label class="crm-quickSearchField"><input type="radio" data-tablename="cc" value="contact_id" name="quickSearchField">{ts}CiviCRM ID{/ts}</label></li> -->
<!-- <li><label class="crm-quickSearchField"><input type="radio" data-tablename="cc" value="external_identifier" name="quickSearchField">{ts}External ID{/ts}</label></li> -->
Looking back at it now, it would have been better to slog through and find the right combination of selectors with jQuery. Perhaps something like this:
CRM.$(function($) {
$('#civicrm-menu #crm-qsearch ul li:nth-child(3)').hide();
});